This article applies to ebikes equipped with Bafang and similar mid motors. The modification presented has been tested in an ebike equipped with a Bafang BBSHD kit only. It should work with other mid motors that have freewheeling chainrings.
The mid drive ebike already has a chainring freewheel, we only need to modify the rear freewheel to get more friction. The method we use to increase friction is to place an insert between the sprockets and the wheel.
We describe below two methods to increase the friction to the freewheel, using a wedge and using a disk.
The insert used should allow the freewheel to spin if forced. If by chance an object is trapped between the chain and the chainring the drivetrain will stop, preventing an accident.
1. Cut a piece of the flexible material about 1 1/2 inches by 3/4 of an inch ( 40 mm by 10 mm), give it a half moon shape as shown in the photo.
2. Insert the wedge into the gap between the large rear sprocket and the hub as shown, the red arrow points to the wedge. Push it down just below the bottom of the sprocket teeth so it clears the chain.
1. Remove the rear wheel from the ebike.
2. Use a freewheel tool to remove the rear freewheel.
3. Cut a disk of the soft material as shown in the photo, the inner diameter should be larger than the hub threads ( or splines in the case of cassette) and the outer diameter should be sufficiently smaller than the largest sprocket so it does not interfere with the chain.
4. Place the disk on the hub as shown.
5. Replace the freewheel. Once tightened try moving the sprockets counterclockwise, they should move with some effort.
6. Replace the wheel